Spray molding process



United States Patent Office Re. 24,351 Reissued Aug. 27, 1957 SPRAYMOLDING PROCESS Andrew Anthony Varela, Costa Mesa, Calif, and Howard T.Bangs, North Plainfield, N. J assignors to American Cyanamid Company,New York, N. Y., a corporation of Maine No Drawing. Original No.2,781,553, dated February 19, 1957, Serial No. 342,272, March 13, 1953.Application for reissue June 14, 1957, Serial No. 666,283

15 Claims. (Cl. 18-60) Matter enclosed in heavy brackets I: appears inthe original patent but forms no part of this reissue specification;matter printed in italics indicates the additions made by reissue.

This invention relates to a process of molding resinous materials. Moreparticularly, this invention relates to a process of molding whereby adurable, protective and decorative design or surface is applied to afusible thermosetting molding composition.

The surfacing of molding compositions whereby a durable, protective anddecorative design or surface is obtained has long been desired. Variousmethods have been employed to surface molding compositions but no methodhas been found to be satisfactory for curved as well as flat surfaces.While surfaces may be applied to molding compositions, such propertiesas water absorption, surface hardness, abrasion resistance, shrinkage,boil resistance, flexural strength and resistance to stoving have beensacrificed. Among the general methods of applying a surface to moldingcompositions are dusting, dipping, spraying and placing a pill preformof surfacing compound on a core preform and then molding. The dustingtechnique is utilized in a two-step molding process for glazing the topsurface of fairly non-complex-shapes such as plates and table tops. Bythis method, a suitable core material is partially cured, the mold thenopened, a layer of surfacing resin dusted on the surface, and the cureof the material then completed. Such a surface, however, does not haveadequate durability to resist cracking during thermal stress. In theclipping technique the base materials are preformed and partially cured.The partially cured article is then dipped into a solution of thecoating resin, dried until the solvent medium has evaporated and thencured in the usual manner. Good coverage of flat surfaces is obtainedbut surface coverage is not satisfactory with complex shapes containingcurves due to the flow of the resin solution prior to drying. In thespraying technique an aqueous solution of the surfacing resin is sprayedupon a preformed object, dried and then molded. The results obtainedwhen the resin solution is sprayed onto the preform are not completelysatisfactory inasmuch as roughness, crazing and cracking occur duringthe cure of the material due to thermal stress set up between the basematerial and the coating material or separation of the surface from thebase material tends to develop. The coating also fails when surfacecracks appear due to flow and spread of the material during the stovingtests. In the pill preform technique the general method is to place acharge in a mold and form a preform. The mold is opened after a setinterval and an electronically warmed pill preform is inserted, the moldreclosed and the cure completed. Objects preparedin this manner do notpass the stoving and acid boil test. In the stoving test the object ismaintained at an elevated temperature for an extended period, e. g. 77C. and 8 hours, to test the surface coverage. The acid boil test alsotests the surface coverage by placing the object in boiling acid for acertain period, c. g. 1% H2804 for 10 2 minutes. Due to the shrinkagedifference between the base material and the coating material, crackingof the surfaces results. Also, the entire surfacing of the object is notalways accomplished.

It is an object of this invention to mold objects possessing a durable,protective and decorative surface coating or design. It is a furtherobject of this invention to produce molded objects possessing a surfacecoating having increased properties of water resistance, surfacehardness, abrasion resistance, shrinkage, boil resistance, flexuralstrength, and resistance to stoving. An additional object of thisinvention is to produce a molded compound having increased colorstability. These and other objects of our invention will be discussedmore fully hereinbelow.

We have found that the above noted and other objects are attained when aresinous product of reaction of an (A) aldehyde, e. g. formaldehyde andan ingredient selected from the group consisting of (B) (1) melamine and(2) a 4,6 diaminotriazine wherein the amino groups attached to thecarbon atoms in the 4- and 6-positions are unsubstituted and the carbonatom in the 2-position has attached thereto a particular kind of radicalas used in the solution and sprayed on the hot mold.

The 4,6-diaminotriazines, which are reacted with an aldehyde, and theresulting aldehyde-reaction product then placed in solution to beemployed in the present invention, may be represented by the followinggeneral formula:

wherein X represents (a) a straight or branched chain, saturated orunsaturated, aliphatic hydrocarbon radical of from 1 to 9 .carbon atoms,inclusive, as, for example, acetoguanamine, n-butyroguanamine,isobutyroguanamine, methacryloguanamine, sorboguanamine,n-valeroguanamine, caproguanarnine, heptanoguanamine, capryloguanamine,4- ethyl-Z-octenoguanamine, etc. or

(b) a cycloa'liphatic hydrocarbon radical as in, for example, A-tetrahydrobenzoguanamine, hexahydrobenzoguanamine, 3-methyl-A-tetrahydrobenzoguanamine, 3- methyl-hexahydrobenzoguanamine, 3,4dimethyl A l,2,5,6-tetrahydrobenzoguanamine,3,4-dimethylhexahydroguanamine, or

(c) an aralkyl radical as, for example, phenylacetoguanamine,tolylacetoguanamine, etc., or

(d) a monoor di-substituted amino group in which the N-substituent orsubstituents are any of the substituents of (a), (b), and (c), above,and, in addition, aryl radicals having not more than 10 carbon atoms, asin, for example, N-butylmelarnine, N-phenylmelamine, benzoguanamine,N-tolylmelamine, N-cyclohexylmelamine, N,N-diallylmelamine,N,N-dibenzylmelamine, etc.

Mixtures of two, three or any other number of different4,6-diaminotriazines of the kind embraced by the above formula andmelamine may be used in place of asingle such triazine if desired.

While we prefer the use of formaldehyde either in aqueous solution or asparaformaldehyde for condensation with the above-indicatedaminotriazines and melamine, other aldehydes or substances yielding analdehyde, e. g., acetaldehyde, propionaldehyde, valeraldehyde, furfural,trioxane, paraldehyde, benzaldehyde, etc., may be employed. The combinedmolar ratios of aldehyde to aminotriazine will vary from about 1:1 toabout 4:1, the preferred range being from about 1.5 :l to about 2.5: l.

reaction is carried out atatmospheric pressure. If higher pressuresareused, the temperature may be increased, but it should not be aboveabout 200 C. The preferred temperature range is generally from about 80C. to about 105 C.

, The-resin solution is sprayed on the hot mold, maintained. onsaidhot-mold-for'a certain period, and then transferred to become anintegral part of a basematerial which is placed in the mold and moldedin the'usual process, The solution of the resinthat is sprayed on thehot' mold 'may be applied to either the male; female or' both-members ofthe mold; By this process curved surfaces,- -as-,well as flat surfaces,may be coated. A most striking appearance is given to; the moldedobject'by incorporating pigments and/ or dyes into the solution of thecoatingjresinp Accordingly, it is usual to disperse and/or dissolvepigments ajnd/or dyesinto the solution of the coating resin. Suchpigments as cadmium yellow, cadmium red, cadmium maroon, titanium oxide,black iron oxide, chrome green, gold, silver, aluminum, copper and pearlessence may be dispersed in the solution to impart any'desired color ormetallic eifect to the molded object. Such dyes as alizarine red,Prussian blue, auramin, naphthol yellow, malachite green may also bedispersed or dissolved in the solution to give any desired color to thesolution. Any amount of pigment that will remain in suspension untilsprayed may be employed. Also, any amount of dye that remains insolution until sprayed may be utilized. It is preferred, however, thatfrom about 10 to about 20 parts of the mixture of dyes and/ or pigmentsbe employed per one hundred parts of solvent. While it is not necessary,from 1to 5 drops ofa we'ttin'gagent such as dioctyl sodiumsulfosuccinate, diamyl sodium sulfosuccinate, dihexyl sodiumsulfosuccinate and the like, may be added' -to' the solutiontoinsure'thorough wetting-and dispersion of the pigment therein. The'mel'amine-forr'nal'dehyde resins,- 4,6-diaminotriazine aldehydereaction products or mixtures thereof that are'added' to the'solutionmay be varied'from about 5' parts "toabout 35 parts in 100 parts ofthe'solvent'. However, it is "preferred that from about 20 to'about' 25parts of the resin be-employed' per 100parts' 'of solvent. Water,alcohol or amixture' of water and any-of the lower aliphatic water'soluble alcohols such as methanol, ethanol, propanol; 2 and'3 butanolor mixtures thereof serves as the solvent depending upon the resinousmaterial employed. Othe'r solvents which may also find'use in'theprocess are benzene, n-butanol, acetone, xylene and the like. While allwater may be employed 'in preparing the resin solution or emulsion,thepercentage ratio of waterto alcohol in the solution when such amixtureis used may vary from about 80:20 to about 20:80, respectively.If desired;any acidor acid producing substance such'as hydrochloricacid,'-acetic acid or phthahc anhydride' and the like-maybe added as acatalyst to the resin solution to-shorten the cure time of the coatingfilm.

The resins utilized in the solution may be prepared as set forthin thefollowing examples; All 'parts' given' are parts by weight and shouldnot be considered critical unless otherwise indicated in theappendedclaims:

RESIN A A melamine formaldehyde resin was repared as fello'wst Into asuitable reaction'vessel was charged 126 parts of melamine and'l62 partsof formalin (37% aqueous formaldehyde) and the pH of the solution wasadjusted-to-7.0 with sodium hydroxide solution. The reaction mixture wasthen heated to reflux temperature and reacted at this temperature for aperiod of 20 minutes. The pH of the reaction mixture was then adjustedto 10.0 and the mixture cooled to room temperature at which'time thereaction mixture" was then spray dried and the resinousmaterialcollected.

In the production of the melamine formaldehyde resin from 1 mol to 6mols of formaldehyde may be reacted per mol of melamine to produce asuitable-resin to be employed in the process of our invention. However,it is preferred that from 1.5 mols to 3 mols of formaldehyde per mol ofmelamine be employed in the preparation of the resin utilized in ourprocess.

RESIN B A be'nzoguanamine melamine formaldehyde resin'was prepared asfollows:

184 parts of benzoguanamine, 192 parts of melamine and" 335 parts "offormalin (37% aqueous formaldehyde) are inti'd lced info a suitablereaction chamberequippedwith thermometer, stirrer, and reflux condenserand mixed; for approximately '5 minutes. The pH is adjusted 6.2-6.6using .sodiumhydroxide solution. The reaction mixture is then heatedto'reflux in 25-35 minutes and refluxing-is contiiiued'until 'the'resinhydrophobes in the kettle. The syrup thusp'r'odu'ced is cooled to 60-65C. in 10-20 minutes. There is then' added'289 parts of a 60% aqueous,

butanol solution thoroughly mixed with the syrup and filtered."

The benz'oguanamine melamine formaldehyde resin shouildihave' presentmelamine and benzoguanamine ina mol ratiowithin the range of 1:2 to33:1, respectively,- and preferably 1.6:1, respectively. It is furtherdesired that'tlieratio of'benzoguanamine and melamine to ftn'maldehyde"in the'resin be within the range of 111.5 and 1: 2. 1, respectively, andpreferably 1:1.5, respectively. The employment of such a resin as asurface'coating is desirable inasmuch as improved coifeestain'resistance is N,N-diallylmelamine and formaldehyde: are

charged to a suitable vessel equipped with meansfor,

reflux,,and'thesodium'hydroxide'is added to give a slurry pH'of8l0f. Thereaction mixture is heated to reflux in 36 minutes and held'at reflux,98 C. for 55 minutes.

At' this 'pointthe' solution becomes'turbid and hydropho- It is vacuumconcentrated:

bio, and has alpH of 8.5. at 240 mm. mercurypressure until the batchtemperature reaches C., and then at 160 mm. mercury pressure for 50minutes until the temperature reaches C.

The rejsinf'is dumped onto trays, cooled and ground. A 50% solution ofthis resinin ethanol is stable at 2025 C. for more than 5 hours.

The 'base mat'erial utilized in our invention may be; any of thefusible-thermosetting resinous materials suchas the phenolics, e. g.phenol-formaldehyde resins, phenolfurfural' resins; theurea resins, e.g. urea-formaldehyde, urea-melamine-formaldehyde; the triazine resins,;-e.; g;- nielamine-formaldehyde, benzoguanamine-formaldehyde andpolyester molding compounds, aniline formaldehyderesifis', epoxy resins,and the like. The base material may? be either filled or unfilled.Suitable fillers are such materials as alpha cellulose, wood pulp,chopped rags, wood flour, glass fibers and asbestos. The base materialmay be charged into the hot mold in any desired manner, as for examplecold granular. resinous material, high frequency or otherwise prewarmedpills, and resin impregnated preforms. When the base material is curedin the usual manner, the film of coating resin that has been sprayedonto the hot mold then transfers to and becomes an integral part of themolded object. Molded objects containing this coating are superior insuch properties as water absorption, surface hardness, abrasionresistance, shrinkage, boil resistance, flexural strength, andresistance to stoving than are surface coatings applied to a basematerial by any previously known method.

In the process of our invention the solution of the coating resincontaining the desired pigments and dyes is sprayed onto the hot moldmaintained at a temperature of about 300-350 F. whereby a film of saidmaterial is deposited on the hot mold. The thickness of the film mayvary over rather wide limits. When special effects are desired, it isnot necessary to spray a film over the entire mold area. to .show thebase material through the film, a clear solution of the resin will besprayed upon the mold to form a very thin film. For complete coverage ofthe base material a film thickness varying between about 0.001 and about0.008 inch is desirable with a film thickness varying between about0.003 and 0.005 inch preferred. If too thick a film is applied, atendency for the surface to craze during testing develops. The film ismaintained on the hot mold at least long enough for the solvent mediumto evaporate therefrom. If articles such as buttons are to be coatedwith the resin film, the film is maintained on the hot mold for a periodof from about 45 to about 60 seconds before the base material is chargedinto the mold and the curing of the finished product accomplished. Ifarticles such as dinnerware are to be coated with the film, the film ismaintained on the hot mold for a period of from 3 to minutes before thebase material is charged into the mold and the curing cycle completed.The period of time that the film is maintained on the hot mold is suchthat the film adheres .to the mold but still is soft enough to transferto and become an integral part of the molded object. As previouslystated, the time the film is maintained on the hot mold may be reducedby the addition of an acid or acid producing substance to the resinsolution. If the film is maintained on the hot mold for an insufiicienttime, it will disintegrate during the molding process Whereas if thefilm is maintained on the hot mold for too long a period, the film willcure to such a state that it will not adhere to the molded object. Alsothe surface would be rough and dull. As previously stated the film maybe sprayed on either the male, the female or both members of the mold.

The molding process employed may be a conventional compression typeoperation. Any molding process Whereby any or all of the hot mold partsmay be spray coated with the resin coating film, as for example transfermolding, plunger molding, etc., may be utilized in our invention. Eithercold granular, prewarmed or impregnated preforms of a fusiblethermosetting resinous material may be employed as the base material. Ina typical molding cycle from about to about seconds closing period ofthe mold with approximately a 5 seconds breathe of the mold is utilized.By employing a high frequency prewarmed pill, a cure time varying fromabout 2% to about 3 /2 minutes at 320 F. with a pressure varying fromabout 2200 to about 7000 p. s. i. give satisfactory results. The curetime and the mold pressure will, of course, vary depending on the amountof base material charged into the mold. For example, a large dinnerplate to be transformed into an infusible and insoluble state willrequire approximately 2800 p. s. i. mold pres sure and 3% minutes curetime at 320 F. whereas a At other times when it is desiredsalad platewill cure at this temperature and time at approximately 2200 p. s. i.mold pressure. Intricate shapes such as cups including a handle thereforrequire greater mold pressures to cure. In order to expedite the moldingprocess it is conventional to employ a high free quency prewarmingdevice. By placing a pill of the resinous material in a prewarmeroperated at tempera tures from 200 to 250 F. for a period fromapproximately 15 to 60 seconds, a reduction in cure time of the moldedobject is obtained. 7

Generally, the solution of the pigmented resin sprayed onto the hot moldis uniformly applied. If desired, however, by the utilization ofstencils, decorative designs, such as monograms, bands and the like maybe applied to the base material. Inasmuch as the fihn is transferred toand becomes an integral part of the base material, such undesirablefeatures as taste, odor, water resistance, etc. of the base material maybe overcome by the process of our invention when otherwise theseundesirable properties of the base material prevent the utilization ofsuch materials in molded objects as for example dinnerware. In orderthat those skilled in the art may morefully understand the inventiveconcept herein presented the following examples are set forth. All partsgiven are parts by weight unless otherwise indicated and should not beconsidered limitations unless noted in the appended claims.

Example 1 An aqueous alcohol solution was prepared by comixing 50 partsethanol, 50 parts of water, 20 parts of Resin A and 20 parts of apigment dye mixture containing 10 parts of gold pigment in combinationwith 3 drops of dioctyl sodium sulfosuccinate as a wetting agent. Theresin solution was sprayed onto the male member of a hot mold thetemperature of which was 320 F. and was maintained thereon for a periodof 5 minutes. A melamine formaldehyde resin pill pre-warmed in a highfrequency prewarmer for a period of 30 seconds and to a temperature of220 F. was charged into the mold and the mold closed and the materialcured at a temperature of 320 F. for a period of 3 /2 minutes and at amold pressure of 2800 p. s. i. Upon removal of the plate from the moldit was found that the film had transferred to and become an integralpart of the object. The surfacing was complete and uniform and nofailures were observed therein after subjecting the molded object toacid boil and stoving tests.

Example 2 When a similar experiment was made employing a pigmentedaqueous alcohol solution of Resin B coating, comparable results wereobtained.

Example 3 N 41-NH:

N UN-ii in which X is a substituent containing no more than 10 carbonatoms of the group consisting of aliphatic hydrocarbon radicalscontaining from 1 to 9 carbon atoms, cycloaliphatic hydrocarbonradicals, aralkyl radicals, aryl radicals and NR R wherein R and R eachis a substituent of the group consisting of said hydrocarbon radi- IdLQsfi bstantiaIly;egaporating the splventth'ere- "to pgqdnce azfilm ofthickness not substantially excontaining a fnsiblethermcsettingrresin10f. the group consisting of phenolic, urea,triazinqpfllyester; anilinewm dshy sl a dspp res n .a 't r r moldingtheistate i hjch; the filrn does not disintegrate l t s flow ,d t n thcqui tmoldi'ns ib i st 'be pn s state wh ch he-film. is

'ble to hond int'egrallyto said charge durocess acgor ding-to claim '1in which the aldehyde t m d h d a ace d' g-; to claimu1 in whiclrthecondeiisatfe c mpi isesfa melamine formaldehyderesin 4; A pr essaccordingatoclaiml in which the conde'ff e' co pr ises a benzoguanaminemelamine formaldehydre sinl S. A process according to claim ,1 in whichsaid charge is an unheated granular'rsin coniposition.

6 A process -according-to claim 1 in'which said charge is a prewarine iresin) composition,

Aprqcess aceording-, to claim 1 in which thecondensa'teis,a;melamine.forrnaldehyde resin and said charge is a'prewarmedresincompositiom;

8 A process a, =.0 rdingto claim- 1 ,in which the: con? densate, is abenzoguanamin'emelamine formaldehyde resin and said-charge is-aprewarmedresin composition.

abontfl D inc-h; partially and substantiallys uni uring th n1,introducing i nto themolda charge r al article by the application- Ofhar ge andthe film withthe mold which process said partially cured film,is cured according-to claim l in solution contains ahpigrnentdispersedtherein- V H 1 A IPIQQQSS 9 1 -t a w ch hcrresin:

solution contains a melamine formaldehyde resin, a curing 1 catalyst forsaid resin and a pigment disperseditherein.

12', A processaccordingto claim 1 irrwhichthv resin solution contains abenzpguanaminefmelamine formaldea hyde resin, a curingcatalyst for saidresin and a pigment dispersed therein, e u 13. A process according toclaim 1 inwhich saidcharge comprises a melamine formaldehyde resin, y g

1 4. A'process according -to clairn 1 in which. the resin solutioncontains a melamine formaldehyde; resin, acuring catalyst for saidresin" and a pigment dispersedinan aqueous lower aliphatic alcohqL-andsaidrcharge com prises aprewarmed" melamine formaldehyderesing, l5 Aprocess according-to claim 1 inwhich the, resin solntion contains a benzognanamine melamine formalde-. hyde resin; a curing; catalyst for saidresin and a pigment dispersed in an aqueouslower aliphatic alcohol, andsaid charge comprises'a prewarmed melamine formaldehyde resin.

nfiii'es' Cited iii tlie'Iffleo f this patent orthe original patentUNITED STATES PATENTS process according;toelaim lgin the

